(a) Field of the Invention
The present invention relates to an apparatus and a method to obtain continuous undisturbed sampling, and particularly, but not exclusively, from a heterogeneous granular till soil.
(b) Description of the Prior Art
Sampling non-plastic granular till has always proven to be a problem as precise sampling thereof has never been adequate. Many geotechnical problems are connected with the construction of earth dams, highways, buildings, or other structures in or on such type soils. It is known in the art that granular basal till is an excellent foundation stratum and also an excellent construction material often used in the construction of dam cores (if the percentage of silt is over 15%). The difficulty in obtaining samples of granular till is due to its heterogeneous granular composition of silt, sand, gravel, and stones of all sizes with non-plastic characteristic. In order to satisfactorily determine the geological and geotechnical characteristics of such soil deposits, it is essential to obtain sampling with as high recovery as possible.
The common method used to sample such soil is known as the SPT (Standard Penetration Test). The method consists in driving a casing by percussion or rotation into the soil while utilizing water as a fluid to permit the displacement of particles in the area of advancement of said casing. At predetermined depths, usually 1.5 meters, a thick-walled split-spoon sampler is driven below the casing to take a sample. This method has not been found satisfactory as the sample is disturbed and the recovery is very low, thus giving false information as to the exact nature of the soil composition. The presence of cobbles and boulders and the density of the granular till make it very difficult and often impossible to drive the sampler into the ground. Still further, the utilization of water as a drilling fluid washes away the fine particles (silt and sand) present in this soil and thus disturbs and modifies the composition of the soil at the bottom of the casing (sampling depth). In conclusion, this method has not been found adequate. The information obtained is very difficult and often impossible to interpret.
Other techniques of sampling such heterogeneous granular till have been tried but have thus far proven unsuccessful and very costly. For example, the granular till composition can be determined by excavating trenches therein. The disadvantage of such method is that the excavating equipment is limited in depth. Further, because of the large size of such equipment, they often cannot be brought to the site where the excavation is required. Seismic techniques have also been tried to obtain some definition of the lithology of the granular till. However, such techniques also cannot give a precise enough geotechnical information of the formation of the granular till.
No one has heretofore been able to obtain an undisturbed continuous sampling of non-plastic granular till soil.